Semiconductor device substrate and process for preparing the same

Abstract

A process for preparing a semiconductor device substrate comprises a step of making at least one surface of a first substrate composed of Si material porous, a step of oxidizing inside walls of pores in the resulting porous Si surface layer, a step of forming a monocrystalline Si layer on the porous Si surface layer, a step of bonding the monocrystalline Si layer to one surface of a second substrate through an insulating layer therebetween, a first etching step of removing the first substrate by selective etching except for the porous Si layer, and a second etching step of impregnating the porous Si layer exposed by the removal of the first substrate with hydrofluoric acid or a first liquid mixture of hydrofluoric acid and at least one of an alcohol and a hydrogen peroxide solution, or by buffered hydrofluoric acid or a second liquid mixture of bufffered hydrofluoric acid and at least one of an alcohol and an hydrogen peroxide solution, thereby selectively removing the porous Si layer.

What is claimed is: 
     
       1. A process for preparing a semiconductor device substrate which comprises a step of making at least one surface of a first substrate composed of Si material porous, a step of oxidizing inside walls of pores in the resulting porous Si surface layer, a step of forming a monocrystalline Si layer on the porous Si surface layer, a step of bonding the monocrystalline Si layer to one surface of a second substrate through an insulating layer therebetween, a first etching step of removing the first substrate by selective etching except for the porous Si layer, and a second etching step of impregnating the porous Si layer exposed by the removal of the first substrate with hydrofluoric acid or a first liquid mixture of hydrofluoric acid and at least one of an alcohol and a hydrogen peroxide solution, or by buffered hydrofluoric acid or a second liquid mixture of buffered hydrofluoric acid and at least one of an alcohol and an hydrogen peroxide solution, thereby selectively removing the porous Si layer. 
     
     
       2. A process according to claim 1, wherein the second substrate is composed of Si material. 
     
     
       3. A process according to claim 1, wherein the second substrate is composed of a light-transmissive material. 
     
     
       4. A process for preparing a semiconductor device substrate which comprises a step of making at least one surface of a first substrate composed of Si material porous, a step of oxidizing inside walls of pores in the resulting porous Si surface layer, a step of forming monocrystalline Si layer on the porous Si surface layer, a step of bonding the monocrystalline Si layer to one surface layer of a second substrate composed of Si material through an insulating layer, a step of removing the first substrate to a depth just before the porous Si layer is exposed, or to a depth where the porous Si layer is partially exposed, a first etching step of selectively etching the first substrate by etching except for the porous Si layer, and a second etching step of impregnating the porous Si layer exposed by the removal of the first substrate with hydrofluoric acid or a first liquid mixture of hydrofluoric acid and at least one of an alcohol and a hydrogen peroxide solution, or by buffered hydrofluoric acid, or a second liquid mixture of buffered hydrofluoric acid and at least one of an alcohol and a hydrogen peroxide solution, thereby selectively removing the porous Si layer. 
     
     
       5. A process according to claim 1 or 4 wherein the insulating layer is formed on at least one of the surfaces of the monocrystalline Si layer and the second substrate. 
     
     
       6. A process according to claim 1 or 4, wherein the insulating layer is provided between the monocrystalline layer and the second substrate. 
     
     
       7. A process according to claim 5, wherein the insulating layer is a thermally oxidized film, a deposited SiO 2  film, or a deposited Si film, or a multi-layered film thereof. 
     
     
       8. A process according to claim 6, wherein the insulating layer is an insulating thin plate provided between the first substrate and the second substrate to bond to the respective substrates. 
     
     
       9. A process according to claim 1 or 4, wherein the bonding step in carried out by one of anodic bonding, compression, heat treatment and a combination thereof. 
     
     
       10. A process according to claim 1 or 4, wherein the step of making the first substrate porous is carried out by anodization. 
     
     
       11. A process according to claim 10, wherein the anodization is carried out in a HF solution. 
     
     
       12. A process according to claim 1 or 4, wherein the step of oxidizing the porous Si layer is carried out by thermal oxidation, spontaneous oxidation in the atmosphere, oxidation in a washing step with RCA or the like, or a combination thereof. 
     
     
       13. A process for preparing a semiconductor device substrate which comprises a step of making at least one surface of a first substrate composed of Si material porous, a step of oxidizing inside walls of pores in the resulting Si porous surface layer, a step of forming a monocrystalline Si layer on the porous Si surface layer, a step of bonding the surface of the monocrystalline Si layer to one surface of a second substrate composed of a light-transmissive material through an insulating layer, a first etching step of forming an etching resistant mask on the bonded second layer and then removing the first Si substrate by selective etching except for the porous Si layer, a second etching step of impregnating the porous Si layer exposed by the removal of the first Si substrate with hydrofluoric acid or a first liquid mixture of hydrofluoric acid and at least one of an alcohol and a hydrogen peroxide solution or buffered hydrofluoric acid or a second liquid mixture of buffered hydrofluoric acid and at least one of an alcohol and a hydrogen peroxide solution, thereby selectively removing the porous Si layer, and a step of removing the etching-resistant mask and increasing a bonding strength obtained in the bonding step when it fails to reach a desired one. 
     
     
       14. A process for preparing a semiconductor device substrate which comprises a step of making at least one surface of a first substrate composed of Si material porous, a step of oxidizing inside walls of pores in the resulting porous Si surface layer, a step of forming a monocrystalline Si layer on the porous Si surface layer, a step of bonding the surface of the monocrystalline Si layer to one surface of a second substrate composed of a light-transmissive material through an insulating layer, a step of removing the first substrate to a depth just before the porous Si layer is exposed, or to a depth where the porous Si layer is partially exposed, a first etching step of removing the first substrate by selective etching except for the porous Si layer, a second etching step of impregnating the porous Si layer exposed by the removal of the first substrate with hydrofluoric acid or a first liquid mixture of hydrofluoric acid and at least one of an alcohol and a hydrogen peroxide solution or buffered hydrofluoric acid or a second liquid mixture of buffered hydrofluoric acid and at least one of an alcohol and a hydrogen peroxide solution, thereby selectively removing the porous Si layer, and a step of increasing a bonding strength obtained in the bonding step when it fails to reach a desired one. 
     
     
       15. A process according to claim 13 or 14, wherein the insulating layer is formed on at least one of surfaces of the monocrystalline Si layer and the second substrate. 
     
     
       16. A process according to claim 15, wherein the insulating layer in one of a thermally oxidized film, a deposited SiO 2  film, a deposited Si 3  N 4  film and a multi-layered film thereof. 
     
     
       17. A process for preparing a semiconductor device substrate which comprises a step of making at least one surface of a first substrate composed of Si material porous, a step of oxidizing inside walls of pores in the resulting porous Si surface layer, a step of forming a monocrystalline Si layer on the porous Si surface layer, a step of bonding the surface of the monocrystalline Si layer to one surface of a second substrate composed of a light-transmissive material, a first etching step of removing the first substrate by selective etching, a second etching step of impregnating the porous Si layer exposed by the removal of the first substrate with hydrofluoric acid or a first liquid mixture of hydrofluoric acid and at least one of an alcohol and a hydrogen peroxide solution or buffered hydrofluoric acid or a second liquid mixture of buffered hydrofluoric acid and at least one of an alcohol and a hydrogen peroxide solution, thereby selectively removing the porous Si layer, and a step of increasing a bonding strength obtained in the bonding step when it fails to reach a desired one. 
     
     
       18. A process for preparing a semiconductor device substrate which comprises a step of making at least one surface of a first substrate composed of Si material porous, a step of oxidizing inside walls of pores in the resulting porous Si surface layer, a step of forming a monocrystalline Si layer on the porous Si surface layer, a step of bonding the surface of the monocrystalline Si layer to one surface of a second substrate composed of a light-transmissive material, a step of removing the first substrate to a depth just before the porous Si layer is exposed or to a depth where the porous Si layer is partially exposed, a first etching step of removing the first substrate selective etching except for the porous Si layer, a second etching step of impregnating the porous Si layer exposed by the removal of the first substrate with hydrofluoric acid or a first liquid mixture of hydrofluoric acid and at least one of an alcohol and a hydrogen peroxide solution or buffered hydrofluoric acid or a second liquid mixture of buffered hydrofluoric acid and at least one of an alcohol and a hydrogen peroxide solution, thereby selectively removing the porous Si layer, and a step of increasing a bonding strength obtained in the bonding step when it fails to reach a desired one. 
     
     
       19. A process according to any one of claims 13, 14, 15 and 16, wherein the bonding step is carried out by anodic oxidation, compression, heat treatment or a combination thereof. 
     
     
       20. A process according to any one of claims 13, 14, 15 and 16, wherein the step of making the first substrate porous is carried out by anodization. 
     
     
       21. A process according to claim 20, wherein the anodization is carried out in a HF solution. 
     
     
       22. A process according to any one of claims 13, 14, 15 and 16, wherein the step of oxidizing the porous Si layer is carried out by thermal oxidation, spontaneous oxidation in the atmosphere, oxidation in a washing step with RCA or the like or a combination thereof. 
     
     
       23. A semiconductor device substrate prepared according to the process of any one of claims 1 to 22.